Tag Archives: 14FF

Disc Braking a GM 14 Bolt Rear Axle

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Extremely detailed look at how I added disc brakes to the GM Corp 14 Bolt rear axle in the Wolf. Procedure can be used for other rear axles too (D60, D70, etc). Contains hints and tips on other axles. Includes detailed part numbers. Also contains excerpts from Military 14 Bolt maintenance manual on axle shaft R&R and wheel bearing R&R and adjustment.

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Detroit Locker install in GM 14 bolt full-floater

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The GM 14 bolt axle is one of the few axles for which the full Detroit locker does not include a new carrier. I’m not sure why this is, but I can only guess it’s because the carrier is near bulletproof. I can see why because it is basically one solid piece split into 2 halves. I’ve never heard of anyone that’s managed to break one. An alternative to the Detroit locker is the lincoln locker.

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It’s easiest to let the manufacturer, Eaton, explain the advantages of the Detroit Locker. They also refer to it as “NoSPIN” as you will see in the following quote.
NoSPIN maximizes traction by delivering 100% of the torque and power to both drive wheels.  It is engineered to keep both wheels in a constant drive mode, yet has the ability to automatically “unlock” during vehicle turning to permit necessary wheel speed differentiation.  The NoSPIN is “trouble free” and does not require special lubricants or service adjustments.
Here’s what the Detroit locker for the 14 bolt full-floater looks like:

The wing nut you can see is used to hold the unit together during assembly. There is a very strong spring that is part of the unit and you’d never get the carrier assembly back together without the bolt and wing nut. It will be removed before installing the carrier assembly back into the axle.
Enough with the babbling, let’s get started.
First thing I did was to remove the cover. This allows the fluid to drain out as much as possible.

Wait a minute, aren’t you forgetting something Scott? Don’t you need to put the truck up on jack stands, remove the tires, blah-blah-blah? No not really. The beauty of the full-floating axle is you can work on all this stuff without doing all that. Only think you should do is chock the front tires, because Park isn’t going to do you any good without axle shafts or even a ring gear for that matter. Back to work now!
Next thing was to remove the axle shafts. This is accomplished by removing the 8 bolts that fasten the shaft to the hub. Complete removal is not necessary. You only need to pull the shafts out far enough to get them out of the carrier assembly. You’ll be able to tell when this has happened. Here’s how mine looked:

As you can see in the photo, some fluid will drain out, so make sure you have something to catch said fluid.
Now it’s time to remove the carrier assembly. There are adjuster nuts on each side of the carrier assembly and they are used in place of the shims many axles use. The adjuster nuts have many small holes around the circumference. Before going any further, you need to use a scribe to make an alignment mark on the housing and nut. Hopefully my marks show in the picture below:

Now you can remove the retainer bolts the hold the clip which in turn holds the adjuster nut in place. You can see one of the bolts at the bottom of the picture above. Once the bolt is out, you remove the clip.
At this point you may want to rotate the ring gear back and forth to get a feel for the backlash. This is the “slop” you can feel changing the direction of rotation. This will give you a feel for what the original backlash feels like. You can use it as a verification that you reset the adjuster nuts properly. Or that possibly some other problem has occurred.

The next step is removing the bearing caps. Make sure to mark which side they are removed from and the orientation. This is very important because re-installing the bearing caps in the wrong position can cause serious damage to your axle. On top of marking them – I like to use a paint pen or punch marks – you can take a picture to help your memory. Set them aside for final assembly.
Finally, we can remove the carrier assembly. To do this you must loosen the adjuster nuts. Be prepared, the carrier assembly will be ready to just fall out, literally. This is when you need the help of a friend or rig up something to catch the carrier. I just used a screw driver to turn the adjuster nuts. I’m sure there’s some fancy Snap-On tool, but the screw driver worked just fine. Count the number of turns using the scribe marks as reference. If I remember correctly mine took about 2 turns on each side. Once you have them loose enough, the carrier assembly should just drop out. Hopefully not on your feet or any other body part.
Now it’s time to tear things apart further as in taking the carrier assembly apart. In order to do this, you must remove the ring gear bolts. It is necessary to replace the ring gear bolts anytime you take them out.
I was able to do the entire process without removing the ring gear itself from the carrier. It is a little bit of a risk because there’s a chance it could just fall off and potentially be damaged. Once you remove the ring gear bolts, you can easily split the 2 halves apart. Here’s what it will look like with the side and spider gears.

Remove the side and spider gears. Make sure you get the washers out with the gears, if they are left in they will not allow the locker to disengage properly. In the picture below you can see all of the gears and washers that must be removed.

Now set the Detroit Locker into the carrier halves. It just sits into the carrier, nothing tricky here.

Bolt the two halves back together and you’re ready to put it back in the axle. You can see arrows on each half that are lined up for proper re-assembly.

Once it’s together, it’s not easy to see there’s a Detroit locker inside. The only way to see it is through the opening in the picture below.

The ring gear bolts need to be torqued to 120ft-lbs. This is another time you’re likely going to need help. We used a crowbar in one of the crosspin holes to provide counter torque. Another good tip I received is to used a hydraulic press to hold the carrier from spinning.
Now it is time to remove the wingnut and bolt discussed at the beginning of the article. Or you can be a blockhead like me and completely re-assemble the axle and wonder why the axle shafts won’t slide back in. Insert lots of cuss words here plus a few smacks on the forehead.
Third and final time for assistance, slide the carrier assembly back into the housing. While your helper holds the carrier in, turn the adjuster nuts back to their position before removal.
Once the adjusters are in position, install the bearing caps back in their original places. Torque the bolts to 135ft-lbs. Now the adjuster nut retainer clips and bolts can be re-installed. Torque the bolts to 20ft-lbs.
Now you can re-install the axle shafts. Hopefully you removed the bolt and wingnut from the Detroit. It does take a little bit of patience to get them back in. Torque the axle shaft flange bolts to 115ft-lbs.
At this point you will need to jack up the rear of the vehicle in order to do the testing Detroit outlines in the installation procedure. I thought it would be nice to post the procedure in case you have the same situation as me and you don’t have the instructions.

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Installation Test


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Step 1
With the engine turned off, raise NoSPIN equipped driving axle(s) until all wheels are out of contact with any surface.  Place the transmission in gear or park so that the drive-shaft is locked and does not rotate.  Test for forward dis-engagement:
Step 2
With two people, rotate both wheels rearward, as far as possible to lock both wheels
Step 3
With the left wheel securely held in the rearward direction, rotate the right wheel slowly forward. A faint indexing or clicking sound should be heard as the NoSPIN disengages on the right side.
Step 4
With the right wheel slowly rotating forward, the left wheel should be rotated slightly forward. This will lock both wheels.
Step 5
Again, rotate both wheels rearward, as far as possible to lock both wheels.
Step 6
With the right wheel securely held in the rearward direction, rotate the left wheel slowly forward. A faint indexing or clicking sound should be heard as the NoSPIN is disengaged on the left side.
Step 7
With the left wheel slowly rotating forward, the right wheel should be rotated slightly forward. This will lock both wheels.

Repeat steps 2-7 except, test for reverse disengagement.
If the above steps are completed successfully and rotating wheels disengage easily by hand, rotate freely and evenly, lock both wheels when required, and produce a faint indexing or clicking sound, then the NoSPIN is properly installed and is functioning correctly.

Once the testing has been successfully completed, install the cover and torque those bolts to 35ft-lbs.
Refill the axle and you’re ready to wheel!
Driving Characteristics?
A first time driver of this differential will notice some differences compared to driving with a conventional differential.
Turning: An occasional snapping/metallic sound may be heard due to component dis-engagement and re-engagement; transfer of torque from both wheels to one wheel (and back to both wheels) may be noticeable in the feel of steering.
Drive-to-Coast: A metallic sound may be heard due to the normal backlash built into the unit.
Slippery Roads: Vehicles equipped with traction differentials are inherently more sensitive to side slip. Use caution when changing speed on slippery or unstable surfaces; decelerate, but DO NOT APPLY THE BRAKE.
Backlash – How Much? At the tire tread, 1″ to 2″ (at the driveshaft, 30o to 90o) depending on tire diameter and ring gear ratio.
“Locker” In Front Axle? Yes, if front drive can be disconnected – either from inside or outside the vehicle – while driving on hard surface roads.
Tire Pressure? Mismatched pressures mean different tire diameters and different wheel speeds. Recommendation: Keep tire rolling radius (by air pressure) matched within 1/4″ for highway vehicles and 1/2″ for off-road vehicles.
Remove Holdout Rings For Racing To Assure Rapid Engagement? Yes, but operation will be harsher and the unit’s life may be shortened.
Can it Weaken Springs? Yes, but this is rare.

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Installing Disc Brakes on GM Corp. 14 bolt Full Floating Axle

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The following article outlines the procedure I followed for swapping rear disc brakes on my rear axle which is a GM Corp 14blt full-floater from a 1979 K30.

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Many people have asked me, “Why do this?” Well there are a couple of universal reasons;

  • Eliminate the problem of having mud packed in the drums.
  • Remove 100+ pounds of weight from the rear axle.

Aside from those I had a couple of personal reasons;

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  • My rear brakes were pretty much non-existent – as you will see in some following pictures.
  • Maintaining disc brakes is much easier.

If you are reading this article and doing research to do this swap yourself, then I’m sure you’re very familiar with what the rear drums on the 14blt FF axle look like. However, it just does not seem right not to have at least one picture of these big, burly brutes in their full glory.

As the picture above illustrates, the first step is to put the rear axle on jack stands and remove the wheels.
Next remove the axle shafts. This is done by removing the eight (8) bolts from the hub with a 3/4″ socket. They are on there tight and use serrated flange bolts, so make sure you have good leverage. Be prepared for fluid to drain out of the hub after the axle shaft is removed.
This is what the hub will look like now.

The hub on the rear axle is very similar to front axle hubs. There will be 2 spindle nuts with some sort of retainer in between. You will need the appropriate hub socket to remove the nuts. On my axle before remove the outer nut I had to bend the tab back from one of the recesses in the nut, otherwise you can’t get the socket on the nut.

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  1. Remove the outer spindle nut.
  2. Remove the retainer washer.
  3. Remove inner spindle nut.
  4. Remove inner keyed washer.

Now you can pull the drum off. Be aware, they are very heavy so have a good grip and position yourself to be able to safely remove them without straining your back.
You may have a situation where you just cannot get the drum to pull off, like maybe you forgot to remove something. Unfortunately it’s not quite that simple. More than likely the shoes have worn into the drum far enough that a lip has formed on the inside of the drum. This lip is preventing the drum from sliding off the shoes. I had this problem on one side. You must back the adjuster off to allow the shoes to move in. Refer to the picture below: 

  • Yellow finger is pointing to the adjuster – puts tension on the shoes
  • Green finger is pointing to the adjuster ratchet stop – keeps the adjuster from backing off
  • Red finger is pointing to the access hole for the adjuster

Because what I’m calling the “adjuster ratchet stop” keeps the adjuster from backing off, you need to disengage it in order to move the adjuster the correct direction. All of this must be done through the little access hole. Now I don’t know if there is a fancy tool for this, but I used a long, skinny punch to push the stop away (as you are laying under the truck this means towards the end of the axle) and a flat blade screw driver to turn the adjuster. Yes it’s a big pain.
Now hopefully you have the drums removed and you should see the working components of the drum brakes as seen in the picture above. This entire assembly can be removed in one piece. Remove the four bolts you can see already missing in the picture above. Disconnect the brake line from the back of the assembly and it will just pull off with a little effort. The picture below shows what you’ll have after the removal.

You will see the spindle is welded to the axle tube. I would imagine you’d want to take great care not to damage the spindle because I don’t think replacement will be a simple matter.
Now we are ready to install the disc brakes. I’ll start with a list of the parts you will need:

  1. Caliper Brackets – mine are from Ruffstuff Specialties and the following parts are what’s needed for these particular brackets. Verify what parts are needed for the brackets you choose.
  2. Dana 44 Calipers for 73-77 Chevy trucks, 1/2ton or 3/4ton. If you get “loaded” calipers, new pads will be included.
  3. Rotors for 73-77 Chevy trucks front axle, 3/4ton only
  4. Rubber brake lines to fit the calipers. There are many options here, the most common are 73-77 Chevy truck application or 1980 Chevy Chevette application (these are popular because they are shorter).
  5. Brake fluid
  6. Optional items:
  • Proportioning valve – You may find your rear brakes lock up much sooner than the front. This can lead to unstable handling under emergency braking. Installing an adjustable proportioning valve in the rear brake lines will allow you to adjust the bias back to the front brakes.
  • New bolts to mount the caliper brackets: Grade 8, 1/2″ x 1″ NF w/split lock washers – 4 per side
  • New hard brake lines. They are 3/16″ lines and you can choose from assorted lengths at the parts store and bend them to fit how you like.
  • New oil seals for the rear hubs. You have the hubs off, might as well replace them.
  • New axle shaft flange gaskets. They are only $3ea, might as well replace them too.

Let’s start with finishing up the last detail in the deconstruction phase. The drums need to be separated from the hubs. The picture below shows where the two pieces separate: 
In order to do this the studs must be press out. If you don’t want or need to salvage the existing studs, you can remove them with a big hammer. However, if you plan to re-use them you need to use a press. The “cheap” Harbor Freight press I used worked just fine.
Now the rotors can be attached to the hubs by pressing the studs back on. The rotor installs on the hubs just like the drum was. With that done, it’s time to go back to the axle.
The next step is to install the caliper brackets on the axle. I used a little thread locker on the ends of the bolts and installed new bolts with new lock washers. I orientated the brackets so the caliper will sit as it does on the front axle. 
The hub rotor assembly is installed next. The following is the procedure outlined in my Chilton’s book.

  1. Install the thrust washer
  2. Install inner spindle nut and torque to 50ft-lbs while rotating the hub. Loosen the nut and re-torque to 35ft-lbs and finally loosen the nut 1/4 turn.
  3. Install retainer washer
  4. Install outer nut and torque to 65ft-lbs.
  5. Bend one tank into the slot on the outer nut.

Install the axle shafts and torque the flange bolts to 115ft-lbs.
Now the caliper can be installed on the rotors. This procedure is the same as installing them on the front axle with the bleeder screw pointing up. Once the caliper is installed attach the rubber brake line. The rubber brake line can then be plumbed in with the hard line. I ran my lines over the top of the springs and along the axle truss. This way they are up out of the way. 

Just for curiosity sake, here’s a picture with drums on one side and discs on the other.

Bleed the brakes, install the wheels, and you are done with the install. Now go out and test drive.
As I stated earlier, you may find it necessary to install an adjustable proportioning valve for the rear brakes. I am fortunate and my brakes function properly without one. It seems to be one of those things that differs from truck to truck. It may even come down to personal preference.
I had an opportunity to test the new brakes on a snow, slick trail the day after the install. The brakes worked great. A lot of that probably owed to the fact that my rear shoes were virtually gone and therefore I didn’t have much in the way of rear brakes with the drums. I can tell the brakes are better because I found myself stopping much more suddenly given my usual pedal pressure.

Finished product:

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